Reference to related patents and application, assigned to the assignee of the present application, the disclosures of which are hereby incorporated by reference:
U.S. Pat. No. 3,598,212, GIESE. PA0 U.S. Pat. No. 3,702,649, GIESE et al. PA0 U.S. Ser. No. 519,692, filed Aug. 2, 1983, HAGEN & SEBULKE.
1. Field of the Invention
The present invention relates to conveyor apparatus, transport apparatus, and the like, which are operated in one direction, hereinafter the "forward direction" and include a run-back lock or safety mechanism to prevent reverse operation.
2. Description of the Prior Art
Various types of conveyor apparatus, such as belt conveyors, link conveyors, chain conveyors, trolley or tramway systems which may be suspended, or rope or cable-operated or pulled, lift apparatus such as ski lifts and the like, frequently include a run-back locking mechanism, located between the drive motor for the conveyor apparatus and a driven shaft, connected to the drive belt, cable or the like of the conveyor. The run-back safety mechanism prevents reverse operation of the conveyor. In one such safety mechanism, which includes a return stop, a one-way clutch is provided which has a ring-shaped element, for example in form of an outer ring. A circular element is located concentrically with the outer element, and one-way coupling elements are located between the outer and inner ring. The inner ring is coupled to the conveyor or transporter shaft and arranged to permit free running thereof in one predetermined direction, but to cause the coupling elements to engage and lock with the outer ring upon reverse running of the conveyor shaft, and hence of the inner ring. The outer ring, in accordance with customary procedure, is secured in fixed position, for example to the frame of the machine. Upon a tendency or actual operation of the conveyor, and hence of the conveyor shaft in reverse direction, the locking or coupling elements will lock against the outer ring, and prevent such reverse rotation. The respective rings can be self-centering by their respective position within each other.
While the present invention is applicable to various types of transport or conveyor arrangements, the problems which arise in connection therewith, and the solution, will be described with reference to a conveyor having an upper and a lower or reverse run by way of illustration and example.
Conveyor belts which are used, for example, in the mining industry, usually have material such as rocks, coal or the like placed on the upper run of the conveyor belt. It is unavoidable that pieces of rock or other material being moved by the conveyor fall off, and fall on the lower run thereof, typically beneath the upper run, and operating in reverse direction, that is, they are returned by the lower run towards the end sheave, or return drum. If the goods being returned to the return drum are large, and hard, that is, will not crush, they may jam against the turn-around drum, causing excessive friction and wear, and triggering safety devices which stop the conveyor. It has been customary to manually, physically remove rocks, lumps and other pieces of coal or other minerals which may have been supplied and which caused stoppage of the conveyor by wedging between the lower run and the turn-around drum or sheave. Removal, typically, requires forcible removal with a pick axe or the like. As soon as the jam has been removed, the conveyor belt, due to stored elasticity in the upper run and in the drive shaft and drive system, will start to move, even if no drive power is applied. This sudden movement, due to stored elasticity within the lengthy belt elements, cables, and the like in the conveyor, is highly dangerous to the operating personnel, and may lead to severe, sometimes fatal accidents. It has happened that an operator was crushed between the lower run of a conveyor belt and the turn-around drum or sheave.
A reverse or run-back safety mechansim thus should be capable or being released with respect to its locking effect to such an extent that controlled movement of the conveyor permits controlled release of stored energy, that is, energy which has been stored due to sudden stoppage of conveyor operation when elements become wedged between the conveyor and the drum. The difficulty with such arrangements is, however, that the run-back safety mechanism must not be completely released, since, otherwise, the conveyor would run backwardly after removal of wedging interfering materials due to the weight of the material on the upper run of the conveyor, particularly if the conveyor is moving this material against the force of gravity in an upward direction.
Conveyors and other similar apparatus frequently are driven by a multiple drive, for example by being driven from two or more motors, one on either side of the conveyor, and supplied with a suitable step-down gearing. The upper end of the conveyor may be driven by two looping drums, the conveyor belt being deflected several times in order to obtain maximum winding or looping angles of the belt about conveyor drums.
Conveyors which have multiple drives have the additional difficulty that, if the drive power is suddenly turned off, different return torques have to be accepted by the respective run-back safety mechanism. In selected instances it may occur that one of the safety back-up mechanism or back-run locks must accept practically all the resulting torque, and can be overloaded thereby. It may be desirable, therefore, to utilize torque limiting devices in connection with run-back safety mechanisms, or return-stop locks, so that the one or the other of the one-way clutches can move slightly counter the locking direction to equalize torques among groups of such reverse-run locks or clutches.
It has been proposed in connection with hoists, cranes, and the like, to include one-way clutches between a drive motor and a hoist pulley or sheave. Upon lifting of a load, the sheave can run freely and overrun the one-way clutch. To drop a load, the one-way clutch is permitted slippage by not mounting the outer ring of the one-way clutch fixedly on a frame or the like, but rather to incorporate a disk brake or clutch between the outer ring of the one-way clutch and a fixed building construction or a frame. Typically, the outer ring of the one-way clutch includes an outer gearing to which the disk brake or clutch is connected. The construction substantially extends the space requirements of the entire apparatus in radial direction, as well as in axial direction, and must be kept meticuously clean to prevent contamination of the brake portion or lamella, which may reach that part of the system from gearing and other elements. Load dropping brakes on hoists and similar apparatus are not subjected to the type of stresses to which conveyors are subjected and, of course, a load which is being hoisted and stopped suddenly will not continue upwardly against force of gravity, as a conveyor or similar transporter might, which is capable of statically storing considerable dynamic energy.